The present invention relates generally to noise suppression and, more particularly, to noise suppression in a communication system.
Noise suppression techniques in communication systems are well known. The goal of a noise suppression system is to reduce the amount of background noise during speech coding so that the overall quality of the coded speech signal of the user is improved. Communication systems which implement speech coding include, but are not limited to, voice mail systems, cellular radiotelephone systems, trunked communication systems, airline communication systems, etc.
One noise suppression technique which has been implemented in cellular radiotelephone systems is spectral subtraction. In this approach, the audio input is divided into individual spectral bands (channel) by a suitable spectral divider and the individual spectral channels are then attenuated according to the noise energy content of each channel. The spectral subtraction approach utilizes an estimate of the background noise power spectral density to generate a signal-to-noise ratio (SNR) of the speech in each channel, which in turn is used to compute a gain factor for each individual channel. The gain factor is then used as an input to modify the channel gain for each of the individual spectral channels. The channels are then recombined to produce the noise-suppressed output waveform.
The U.S. Pat. No. 5,659,622, to Ashley, both assigned to the assignee of the present application, both incorporated by reference herein, each disclose a method and apparatus for suppressing acoustic background noise in a communication system. The use of wireless telephony is becoming widespread in acoustically harsh environments such as airports and train stations, as well as in-vehicle hands-free applications.
Therefore, a need exists for a robust noise suppression system for use in communication systems that provide high quality acoustic noise suppression.